I've just found out my partner was seeing a bloke for 4years and was still with him until 4months before I had my son.
How do I deal with this and does it mean he is never going to change.

I wouldn't trust him to change. Either it was a one time 'mistake' or it is his lifestyle to be a cheater. You have to determine which it is with him and remember actions speak louder than words.

I'm asumming you stating your husband slept with a man that because that's what bloke mean.

Once trust is broken there's no crazy glue to fix it. You might feel even downer because it's was a man. You can even stay or go but I would leave if it was me. To have someone cheat on you for a number of years prove he don't care about you nor respect you or the marriage. Cheating will be done again and he might be confuse as if he like women or men because at this point he's bi.

If anything don't put yourself down or start second guessing yourself because it's not fault only his. He is a liar and cheat and you don't need this because he shouldn't have done it. Curious to how you found out.

4 years isn't a one time curiousity. He at the very least swings both ways. What should you do? That's hard to say depending on if he really wants to be faithful or not. He clearly wasn't in the past. THere is now a child involved. Not sure in your country (obviously not USA because for terminology used) or what legal support obligations you might be entitled to.

Stay or go but don't let either you or your husband take it out on your child. Some people make bad husbands or wives and make great parents. How old are you and your spouse and how long have you been together?

The fact that it was all still going on whilst you were pregnant... leaves me lost for words,
To be having an affair, whether man or woman when you partner is carrying your child is despicable, no excuse, he should have been by your side not having it off with another party, not a one night stand, 4 years he's got to be joking if he thinks that's normal behaviour for an expectant father.

He,in my opinion thinks he can have his cake and eat it, no I don't think he will change, 4 years is a long time so he must have enjoyed it.

Don't fall for the " i didn't know what i was doing...i wanted to end it but he said he would kill himself..... it just happened.....it's you i really love"etc.etc...

He needs to leave for a while to let you collect your thoughts together.

Whatever you decide,he will always be your son's father and will have to contribute to his upbringing.

Do not fall for the drama that is sure to follow when you confront him... remember all the lies he must have told you and the times he must have left him and came home to lie beside you... a sound foundation for any relationship is built on trust,you have now lost that.

Think hard before you make a discision... but don't do it looking at him through rose coloured glasses.

Goodluck

You are really going to have to watch yourself for sexually transmitted diseases specially AIDS.

I would never have a husband or a partner who was a practising homosexual... or had been a homosexual. Too dangerous.